Method of improving the properties of rubber and product



Patented Mar. 26, 1935 UNITED STATES METHOD OF IMPROVING THE PROPERTIESOF RUBBER AND PRODUCT Willis A. Gibbons, Montclair, N. J assignor, bymesne assignments, to United States Rubber Company, New York, N. Y., acorporation of New Jersey No Drawing. Application March 8, 1930,

Serial No. 434,462

.9 Claims. (01. 18-50) In the preparation and manipulation of raw andreclaimed rubber for the manufacture of rubber or rubber and fabricarticles, certain physical properties are desired, suchas ease ofbreakdown of the rubber on the mill, smooth calendering, and plasticity.In vulcanized articles, particularly those composed of rubber andfibrous material which are subjected to a flexing action in use, such astires, belting andhose, it is desired to obtain the greatest resistanceto separation between the rubber and fibre caused by the flexing action.7

This application is a continuation in part of m co-pending applicationSerial No. 153,736, filed December 9, 1926.

It has been found that raw rubbers which are decidedly alkaline, such asthose to which alkaline materials have beendirectly added, and reclaimedrubbers which have been reclaimed by the alkali process, are deficientin some or all of the properties of easy breakdown, smooth calenderingand extruding, and when such rubbers are incorporated in rubber andfabric articles, the articles are deficient in resistance to flexing.The present invention therefore relates to a method for improving thephysical properties of such alkaline rubber or alkaline reclaim duringits manipulation prior to vulcanization and to improving the flexingability of the vulcanized material when included in a rubber and fibreartiole. The invention is not limited however in its application to suchrubbers, but also decidedly improves the breakdown, calendering andextruding ability, and flexing ability of other rubbers such asall-solids-content-latex evaporated rubbers, coagulated rubbers, and ingeneral those which show an alkaline ash, and it is also applicable tocombinations of any of the above rubbers.

An object of the present invention is to provide a process for obtaininga vulcanized rubber of improved flexing characteristics. Another objcctis to provide a process for softening, and in general improving thebreakdown, calendering and extruding properties of, rubbers duringmanufacturing operations. The invention also resides in the product ofthe method.

The invention consists broadly in incorporating in solid rubber havingan alkaline ash a material, hydrolyzable to produce acid ions capable ofdecomposing alkali proteinates and soaps, in quantity sufiicient toimpart to the water extract of the rubber a pH of 7 or less, working toa smooth, plastic condition, and, if desired, vulcanizing; and it alsoconsists in the products obtained.

While as previously stated the invention is applicable to raw rubber towhich a fixed alkali has been directly added or to an alkali treatedreclaim, it is also. of value in the treatment of any rubbers which showan alkaline ash, such as coagulated rubbers, all-solids-content-latexevaporated rubbers, or mixtures of any of these. In carrying out theinvention there are incorporated with solid rubbers or mixtures ofrubbers as above named, materials which are hydrolyzable to produce acidions capable of decomposing alkali proteinates and soaps, in quantitysufiicient to impart to the water extract of the, rubber a pH of 7 orless; and this may be accomplished (I) by incorporating with the rubbersuitable amounts of non-volatile organic or inorganic acids strongenough to decompose alkali proteinates or alkali soaps, (II) volatilebase salts of such acids, or (III) heavy metal water soluble salts ofacids, organic or inorganic, volatile or non-volatile, which are strongenough to decompose alkali proteinates or alkali soaps. These acids orsalts may be added either as such or in solution, and they may be addedon the ordinary form of roll mill or in a closed mixer.

To illustrate the improvement in handling properties of the raw rubberaccomplished by the invention, 100 parts by weight of raw rubbercontaining 1 part by weight of potassium hydroxide is placed on a mixingmill and allowed to run thereon until it shows some tendency to sticktogether. This rubber is in no sense broken down, as the term isunderstood in the rubber industry, but retains a rough texture, asevidenced by the lumpy surface. Continued mixing does not result in thesmoothsheet which is characteristic of the market grades of pale crepeor fine para. In fact it resembles a rubber stock which has becomeprevulcanized on the mixing mill, that is, a stock which contains anaccelerator so powerful that vulcanization starts before the batch isremoved from the mill. The distribution of 1%, parts by weight ofphosphoric acid in the above alkaline rubber on the mixing mill isaccompanied by a marked change in the outward appearance of the rubber.After the acid has become uniformly distributed throughout the batch,the latter loses its rough surface, takes on the outward appearance ofwell plasticized fine para, and shows an improvement in behavior inmanufacturing operations requiring considerable plasticity, and thevulcanized product has increased flexing capacity.

In the case of pale crepe, smoked sheet and the other softer commercialrubbers, which are known to break down to a smooth state, the inclusionof the acidic material does not give as striking a contrast on themixing mill as in instances where the rubber contains non-volatilealkali. With rubbers prepared by evaporation the length of time requiredto obtain a smooth sheet on the mixing mill is somewhat longer than thatrequired for crepe or sheet, and the inclusion of an acid material inone of these evaporated rubbers cannot always be accomplished rapidlyenough for a considerable reduction of the milling period to beobserved. With rubber containing an appreciable amount of fixed alkalias such, the effect of the acid treatment is clearly observable on themixing mill, for the rubber becomes smooth in very little more than thelength of time required for'crepe or sheet. Without the acid treatmentit is practically impossible to obtain a smooth sheet of such alkalinerubber. The amount of acidic material added may be calculated as thatrequired to neutralize the amount of alkali in the rubber, or to impartthe desired reduced alkalinity or slight acidity. Preferably the acidicmaterials are those which have a hydrogen ion concentration somewhat onthe acid side of 1 x 10- that is pH 7. In the example given above wherernbbe containing 1% or potassi' hydroxide is treated with 1 4% ofphosphoric acid, the pH of the water extract of the rubber aftertreatment is 6.55, indicating that rubber is no longer alkaline butfaintly acid.

As illustrating the improvement in softness and other handlingcharacteristics, when the process of the invention is applied to areclaim, the following example is given:

To 600 gram samples of whole tire reclaim there were added,respectively, 2%, 3, 4, and 5 c. c. phosphoric acid on the mill. reclaimwas one which had been dispersed and then spray dried, and thephosphoric acid was of 35% concentration, sp. gr. 1.7. The degree ofsoftening of reclaim samples increased with the quantity of acid added;they sheeted out smoothly, and in each case the general appearance andbehavior of the bank of stock on the mill was very similar to that ofcrude rubber. This acid treated reclaim was found to tube, calendar andmold in a manner greatly superior to the untreated reclaim. For theabove described particular reclaim about 4 c. c. of acid to 600 grams ofreclaim seemed to give about the best results, but it is obvious thatthe amount of acid to be used will depend upon the acid, the amount ofalkali in the reclaim, and also upon the amount of softening desired forany particular purpose.

As stated above, many alkaline rubbers show an impaired tensilestrength, even though the rate of vulcanization may sometimes beaccelerated by the presence of the free alkali. The acid treatmentherein described has the effect of appreciably increasing the tensilestrength and improving the other physicm properties as well.

Steam treated spray dried rubber l0 Spindle oil. Zinc oxidc HeptaldehSulphur... Phosphoric i Florin! in kilocycles 7. 8 l3 l5. 0 l8. 7 17. 323. l 20. 0 23. 5 l7. 1 2S. 0 20. 2 28. 5

Example 2 Spray dried rubber 100 100 Spindle oil 5 5 Zinc oxide... 5 7Heptaldchyde-ani 111., .ucl. 0, 5 O. Sulphur U Ii. 75 H, Salicylic cid,i 2

Flcxin z in kilocycles 9 V2.2 10.2 T. b 14.8 9. 7 12511 7.5 21.4

Example 3 Monochloroacetic acid. Using a different fabric, and using aformula similar to that given for Example 2, but adding one part ofmonochloroacetic acid in place of salicylic, the following flexingresults were obtained:

( ure Flexim: in kilocyclcs 25. J 70. 1 25. 5 70. 3 l7. 6 57. 2 Q9. 7l4. 2 20. 3 4.1. 0

Pale crepe .31) Smoked sheet 50 5:) Whole tire reclaim (alkali process)75 Whole tire reclaim (alkali process with 1% monochloracctic acid) l 75XX Zinc oxide 3 5 Spindle oil (mineral) 8 s Heptaldehyde-auilineacceleraton. 0 5 I). 5 Sulphur 5 5 5. 5

com: Flexlng in kilocyclcs l7. 5 l0, 5 l9. 5 21. O 20. 1 2G. 6 22. 6 40.2 l8. 7 2'19. 8

The flexing data given in the above examples was obtained by the use ofa test commonly applied in the tire industry, in which alternate pliesof the rubber to be tested and of fabric are built up to the desiredthickness, cut into pads which are usually 5" x 8", and the pads thenvulcanized in a mold. After vulcanization the pads are removed from themold and allowed to stand for about 36 hours, after which they are cutinto strips, usually 8" x l". The strips are then subjected to a flexingtest in which each strip is secured in a machine by its ends while theintermediate portion of the strip "is in contact with a weightedpulley.The strip is then pulled back and forth around the pulley at the rate ofabout 160 cycles'per' minute until separation of' the plies begins, andthe number of cycles required to cause separation of the rubber from thefabric is noted.

In the case of all the'above examples, the fabric plies were madeaccording to the process disclosed in Hopkinson Patent #1,424,020, inwhich the fabric is weftless and consists only of parallel cordsimpregnated with and united by rubber deposited directly from latex, andthe latex used was compounded with spindle oil, formaldehydeethylaminecondensation product accelerator, soap and sulphur. 4 .7

While applicant does not desire to be bound by any theory, it is hisbeliefthat much of the softening effect and improvement in millingqualities of the rubber, and the improvement in the flexing quality ofits vulcanizate, is due'not only to direct neutralization of free alkaliby the added material, but also to its decomposition of alkali salts offatty acidsand possiblyvof certain protein materials present, such asalkali proteinates. It is obvious that to obtain smooth milling andcalendering on the mill, the rubber should tie-- sirably be in acontinuous phase,but it is applicants theory that the presence of thealkali metal soaps and other materials favors the formation of adispersed rubber phase, as for example in the making of rubberdispersions, and hence the presence of such dispersed rubber phase isunfavorable to the ready formation of the continuous phase which isdesirable forgood softening and calendering properties on the mill.Therefore, it is applicant's belief that the fundamental principle ofthe process consists not only in the neutralization of free alkali butin the decomposition of the colloidal protective compounds of thealkalies with fatty acids and perhaps other materials, and the formationof non-protective and non-colloidal compounds. In other words, the freealkali is neutralized and the alkali soaps and proteinates are convertedinto compounds which are neutral or slightly acid, and which are not inthemselves soap-like in character, that is, in the same sense as watersoluble soaps. It is pointed out that crude rubber itself contains from1 to 2% of naturally occurring soap forming fatty acids, and in thecommercial formulas used by a large majority of manufacturers for tiresand other articles there are also added fatty acids. As a result, whensuch rubbers are reclaimed, the fatty acids are present in the scrap andduring the alkali reclaiming process alkali soaps are formed. Tests haveshown that the addition of soap to rubbers reduces the flexing abilityof the vulcanized stock, and tests have also shown that when the alkalisoaps are washed out of reclaims by the use of alcohol, the reclaims areappreciably softer than those which have been washed with water only, asit is difficult to completely remove such soaps by the use of water.

ing by the application of the' process when using volatile base salts ofnon-volatile organic or inorganic acids strong enough to decomposealkali proteinates or alkali soaps, the following examples are given:

Example 5 Spray dried rubber from ammonia latex. 100 100 Zinc oxide 5 5Spindle oil 5 5 Heptaldehyde-aniline accelerator 0.5 0.5 Sulphur 3 75 3.75 Ammonium chlor acetate 2. 0

CURE Flexing in kilocycles Example 6 Ammonium lactate. Using the sameformula as given in Example 5, but substituting 1 parts of ammoniumlactate for the ammonium chloracetate, thefollowing flexing results wereobtained.

Flexing in kilocycles III .The process of the invention may also becarried out by adding to rubber heavy metal water soluble salts ofacids, organic or inorganic, volatile or non-volatile, which are strongenough to decompose alkali proteinates or alkali soaps. As before, thesesalts may be added either as such or in solution. As examples showingthe improvement in flexing ability of rubbers treated according to thismodification of the invention, the following are given:

Example 7 Pale crepe 50 5o Smoked sheet. l 50 5Q Reclaim (alkaline) 7575 Spindle oil 5 5 Zinc oxide l l l 5 5 Heptaldehydeaniline acceleratori. 0. 5 0.5 Zincnitrate 2 CURE Flexing in kilocycles 3 l2. 8 22. 0 4545th, 10.5 27.9 60 45?; 10.8 15. 4 75 45?? l3, 5 9. 7

Erample 3 Pale crepe 50 Smoked sheet 50 50 Whole tire reclaim (alkaliprocess) 75 Whole tire reclaim (alkali process with 2% zinc chloride)- l75 Spindle oil l H 8 s Zinc oxide 5 5 Heptaldehyde-anillne accelerator0.5 0.7 Sulphur 3. 75 3. 75

CURE Flexing in kilocycles 30 45;? ll. 4 10.8 37. 2 16.6 38.0 ll. 7 66.5 12. 2 58.2

CURE

Flexing in kilocycles 1 From latex containing formaldehyde and asulphonated fatty acid.

Example 1 0 Flexing in kilocycles S. 0 27. 6 i. 8 33. 0 (i. 4 56. 7 5. 366. 7 5. l 52. 6

From latex containing formaldehyde and a sulphonated fatty acid.

Example 11 ycpcwciuo vim CURE Flexing in kilocycles {dFroIn latexcontaining formaldehyde and a sulphonated fatty flCl The modification ofthe invention disclosed in the last five examples is specificallyclaimed in co-pending application Serial No. 434,463, filed March 8,1930.

The increase in flexing capacity of articles made according to thepresent invention is most pronounced where the rubbers treated aredefinitely alkaline, such as those to which fixed alkali has been added,and alkali processed reclaims, i. e. vulcanized rubbers which have beenrestored to a plastic condition to render them suitable for re-use inrubber manufacturing operations; but there is also an improvement in thecase of all rubbers showing an alkaline ash, such asall-solids-content-latex rubbers, or with various combinations of any ofthe above rubbers.

The precise amounts of the free acid or salt to be added willnecessarily vary with the character of the mix and the particular acidor salt, and in general, the more alkaline the rubber mix, the greaterthe amount of any given acid or salt will be required, and this amountcan be readily determined by experiment. In case the rate ofvulcanization of a compound is slowed down to any material extent by theaddition of the acids or salts this can be overcome by increasing theamount of accelerator.

It will beseen that by the use of the invention the flexing capacity ofrubber and rubber and fabric articles may be very greatly increased, andas a result either articles of marked superiority in this respect areobtained with the usual stocks, or much cheaper rubber stocks may beused and yet produce flexing capacity equal to or greater than that ofmuch more expensive stocks at present in use. The invention is capableof wide use in the manufacture of all rubber articles where good flexingis desirable, and it is of particular value for use with the usualvulcanized articles of commerce which are built up of layers of fabricand rubber, such as tires, belting, hose, etc. The improvement inmilling properties is another valuable feature of the invention, as thesoftening of the rubber increases the speed of operation; and theuniformity of, and increase in, plasticity is of great importance inextrusion operations and calendering operations, in which latter it isin many cases necessary to calender in thicknesses of a few thousandthsof an inch.

Where the term rubber" is used in the claims without qualification, itis intended to cover reclaim.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A method of improving the physical properties of rubber before andafter vulcanization. which comprises plasticizing a. body of solidrubber by adding at the beginning of its breakdown a water solublematerial hydrolizable to produce acid ions capable of decomposing alkaliproteinates and alkali soaps, suificient of said material being added toreduce the pH of the water extract of the rubber at least to neutrality.

2. A method of improving the physical properties of rubber before andafter vulcanization, which comprises incorporating in a body of spraydried rubber derived from ammonia latex, during breakdown, a watersoluble material hydrolizable to produce acid ions capable ofdecomposing alkali proteinates and alkali soaps, sufiicient of saidmaterial being added to reduce the pH of the water extract of the rubberat least to neutrality, mechanically working the rubber to a smooth,plastic condition, incorporating it in a rubber and fibre article, andvulcanizing.

S. A method of improving the physical properties of rubber before andafter vulcanization. which comprises incorporating in reclaimed and rawrubber giving an alkaline ash, during breakdown, a water solublematerial hydrolizable to produce fixed-acid ions capable of decomposingalkali proteinates and alkali soaps, sufficient of said material beingadded to reduce the pH of the water extract of the rubber to not morethan approximately 7, reducing the rubber to a smooth, plastic conditionby mechanical working, and forming and vulcanizing a rubber and fibrearticle from the mixture.

4. A method of improving the physical properties of rubber before andafter vulcanization which comprises plasticizing a body of solid rubberby adding during milling a non-volatile acid strong enough to decomposealkali proteinates and soaps, in quantity sufiicient to reduce the pH ofthe water extract of the rubber to at least approximately neutrality,and'reducing the rubber to a smooth plastic condition by mechanicalworking.

5. A method of improving the physical properties of rubber before andafter vulcanization,

which comprises incorporating in a body of spray dried rubber derivedfrom ammonia latex, during breakdown, a non-volatile acid strong enoughto decompose alkali proteinates and soaps, and in an amount sufiicientto reduce the pH of the water extract of the rubber at least toneutrality, reducing the rubber to a smooth, plastic condition bymechanical working, and forming and vulcanizing a rubber and fibrearticle from the mixture.

6. A method of improving the physical properties of rubber before andafter vulcanization Which comprises incorporating in reclaimed and rawrubber giving an alkaline ash, during breakdown a water solublenon-volatile acid strong enough to decompose alkali proteinates andsoaps, and in an amount sufficient to reduce the pH of the water extractof the rubber below 7, reducing the rubber to a smooth, plasticcondition by mechanical working, and forming and vulcanizing a rubberand fabric article from the mixture.

7. A method of improving the physical prop erties of rubber before andafter vulcanization which comprises incorporating in a body of solidrubber before vulcanization and at the beginning of its breakdown aplasticizing agent comprising a strong organic acid selected from thegroup consisting of salicylic, mono-, di-, and tri-chlor acetic, oxalic,citric, lactic, tartaric, and beta napthalene sulphonic acids, in anamount sumcient to reduce the pH of the water extract of the rubber atleast to neutrality, reducing the rubber to a smooth, plastic conditionby mechanical working, and forming and vulcanizing a rubber and fibrearticle from the mixture.

8. The plastic product of an alkaline-ash solid rubber plasticized atthe beginning of its breakdown by the addition of a fixed water solubleacid strong enough to decompose alkali proteinates and alkali soaps, thepH of the water extract of said product not, exceeding approximately '7.

9. The plastic product of the mixture of raw rubber and alkalinereclaim, plasticized in the presence of a fixed water soluble acidstrong enough to decompose alkali proteinates and alkali soaps, the pHof the water extract of said product not exceeding approximately 7.

WILLIS A. GIBBONS. I

